Recently, as high-performance instrument having a built-in actuator has been widely used in fields of medical instrument, analytical instrument, or micro-machine, a small-sized micromotor has been demanded.
In the implementation of the micromotor having a small size, particularly, a small diameter, a coil built in the micrometer is necessarily formed in a small size and finely.
Generally, the coil is formed by winding a copper line which is coated with an insulator such as polyurethane around a core having a slot. Otherwise, the coil may be formed as a coreless coil. Namely, a self-fusing copper line is prepared by additionally forming a fusing layer on the outmost layer of the insulator-coated copper line. The coreless coil is obtained by forming the self-fusing copper line in a shape of cup or bell. In order to implement a cylindrical micromotor having a small diameter, the coreless coil, that is, a coil having no core is very suitable.
Conventionally, as shown in FIG. 3, a Kodak type winding method or a Faulhaber type winding method is used to manufacture the cup-shaped coreless coil. In Japanese Patent Application Laid-Open No. 2004-007938, there is disclosed a parallel coil which is formed by arraying a plurality of the coils that is manufactured according to the aforementioned method in order to minimize current consumption and improve torque characteristic.